Parkinson's disease (PD) is a common neurodegenerative disease of unknown cause. As many as 1.4% of persons over 55 years old and 4.3% of persons over 85 years old are affected. Evidence is accumulating that defective energy metabolism plays a major role in PD. A great deal of interest has recently focused on the mechanisms by which impaired energy metabolism might lead to cell death. Both oxidative stress and excitotoxicity have been implicated. Though there is evidence to support these hypothesis, it has yet to be firmly established that either oxidative stress or excitotoxicity due to impaired energy metabolism plays a causative role in idiopathic PD. These issues will be addressed in this proposal by studying markers of oxidative stress and analyzing neuroprotective measures in vitro in cytoplasmic hybrids ("cybrids") of patients with PD. Cybrids are formed using platelet mitochondria DNA to repopulate a human neuroblastoma cell line containing no mitochondrial DNA. This allows the study of the functional significance of defects in mitochondrial DNA while controlling for potential nuclear DNA factors that might influence mitochondrial function. The specific aims of his proposal are as follows: 1)to analyze the PD cybrids and aged-matched controls for evidence of oxidative damage to DNA, proteins, and lipids by measuring 8-hydroxy-2-deoxyguanosine, protein carbonyls and 3-nitrotyrosine, and malondialdehyde, respectively, and to correlate these findings with clinical features of disease. 2) to determine whether exposure of the PD affected cybrid cells to the mitochondrial toxin MPP+ is associated with increased oxidative damage. MPP is the active metabolite of MPTP, a neurotoxic compound commonly used in animal models of PD. 3) to analyze enhancers of mitochondrial function, antioxidants, inhibitors of nitric oxide synthase, and inhibitors of poly- ADP-ribosylation for their ability to protect against intrinsic oxidative damage and cell death as well as that induced by MPP+ in these PD cybrids. Though several symptomatic therapies exist, no current treatments have been shown to be effective in slowing the progression of PD. The proposed studies will assess the role of oxidative stress due to impaired mitochondrial function, and provide an in vitro assay for testing novel therapeutic strategies that may ultimately slow the process off neuronal degeneration in PD.